Heory, I like your order of reactions better. The ketone formation in yours makes alot more sense than in mine. A couple of things though, I think you lost a carbon when you formed the beta-lactam (should be gamma I think), and your arrows for addition of the enolate to the iminium ion are the wrong way round.

Hello!Dan! i agree with your steps except the sulfur ylide make the addition to the ester group.Heory's 1,3 dipole cycloaddition is more better.but other steps is so excellent! i feel excited about your mechanism.When i read this question,i am wondering why the nucleophlie must attack the same face as the -COOMe?Could you explain it in more details?

Calculated by computer, the trans-substituted lactam has the energy 63kJ/mol more than the cis-substituted one.I think the cylohexone ring is hard to twist because 3 bonds should be at the same plane due to the aryl ring.

Heory get's it right this week. I thought the mechanism might be too ambiguous without the product, but perhaps it was too straightforward with the product given?

I'd also call the cycloaddition a Diels-Alder, but they're just resonance structures of each other, right? The neutral resonance structure is probably the better resonance contributor, but the dipolar cycloaddition is still a resonance structure. The reaction is drawn in the papers as a Diels Alder.

This is methodology from the Padwa group as an entry into the Erythrinane family. Nice work, imho.